1. Field of the Invention
This invention concerns a control device for an electric circuit.
2. Description of the Prior Art
Electrical apparatus are known to generally affect the operating conditions of the circuit to which they are connected. In particular, it is known that high inductance devices such as lamps cause a lead which, in order to avoid disturbances in the power supply network, must be offset by suitable lag-inducing elements, such as by one or more capacitors connected to the device's terminals.
In some cases, the device's effect on the supply circuit varies according to the operating conditions of the device itself. Thus, in the case of a discharge lamp, inductance is high only when the lamp is lighted. Consequently, as long as the lamp is unlighted, the reactive power provided by the capacitor is not compensated, resulting in disturbances in the network whenever the discharge lamp is connected to the network but not lighted.
Moreover, a discharge lamp will not light unless the gases contained therein have cooled. Accordingly, in the event of a temporary mains outage, discharge lamps go out and cannot come back on for a certain lapse of time during which the capacitors create a disturbance in the network. Obviously, in the case of public lighting systems where a large number of discharge lamps are connected to a common supply line, a brief outage causing the lamps to be extinguished subsequently causes a major disturbance which must be compensated by boosting the power supplied to the network. Otherwise, the reactive power of the capacitors is not compensated and the discharge lamps cannot relight.